RE: 8539 obs March 12

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Thu Mar 12 2009 - 07:19:58 UTC

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    Steve Newcomb wrote:
    
    > 11731 80 019C   8539 G 20090312010939210 17 25 0349187+240820 38  
    > 11731 80 019C   8539 G 20090312010950180 17 25 0356759+224216 38  
    > 11731 80 019C   8539 G 20090312011044540 17 25 0428751+154677 38  
    > 11731 80 019C   8539 G 20090312011120140 17 25 0448326+105394 38  
    > 11731 80 019C   8539 G 20090312011127830 17 25 0452280+095205 38  
    > 11731 80 019C   8539 G 20090312011207640 17 25 0511973+042595 38  
    > 11731 80 019C   8539 G 20090312011253460 17 25 0532454-013577 38  
    > 
    > 11731 was 9 seconds early on 09041.75827881 elset
    
    Here is an update:
    
    NOSS 1-3 (C)                                            467 X 1727 km
    1 11731U 80019C   09071.02140479  .00000350  00000-0  63274-4 0    02
    2 11731  63.3757 297.7871 0843131 357.2612   2.3879 13.42992075    04
    
    The NOSS orbits exhibit interesting perturbations due to the effect of the odd
    zonal harmonics of Earth's gravity field on orbits inclined near 63.4 deg: their
    orbits become more elliptical over time.
    
    The initial operational NOSS orbits are approximately circular, about 1110 km in
    altitude, and inclined 63.4 degrees. Mike Waterman rescued the following old
    elset from his paper archives, issued via NASA/GSFC, early in the life of 80019C
    (a few months before the orbits became secret):
    
                                                           1076 X 1142 km
    1 11731U 80019C   83017.99300090  .00000019  00000-0  34724-4 0    07
    2 11731  63.4780 238.4988 0043951  53.7990 306.7086 13.39856952    01
    
    Notice how the orbit has evolved over some 26.1 years: the size of the orbit has
    contracted only slightly, but its eccentricity has grown significantly, from
    0.00439 to 0.08431. As a result, its long axis has been stretched, so that the
    perigee height has decreased by 609 km, but the apogee has increased by almost
    as much, about 585 km (the difference is due to drag, which mainly affects the
    apogee, until an orbit is close to decay).
    
    This relentless stretching - about 24 km annually in both directions, is the
    main reason that the NOSS orbits require so much effort observationally and
    analytically; else, we would soon lose them.
    
    Modern NOSS satellites mitigate this effect somewhat by launching into an
    initial orbit of argument of perigee near 180 deg, which causes the eccentricity
    to initially decrease. In the case of the 3rd generation NOSS, their initial
    1000 x 1200 km orbit becomes nearly circular at about 1100 km, about 4 years
    after launch. By that time, the argument of perigee will have precessed to about
    90 degrees, whereupon the eccentricity begins to increase, such that the initial
    1000 x 1200 km orbit is restored about 8 years after launch. In this way, the
    orbit naturally remains within 100 km of circular, for eight years, which
    presumably is the approximate design life of the satellites.
    
    The NOSS 3-1 satellites achieved their operational orbit early in 2002, and will
    complete their nearly 8 year round-trip in eccentricity in the fall of 2009:
    
    NOSS 3-1 (C)                                           1016 X 1197 km
    1 26907U 01040C   02093.92842396  .00000120  00000-0  20947-3 0    07
    2 26907  63.4290 131.4591 0121000 179.2166 180.7834 13.40414389    08
    
                                                           1103 X 1110 km
    1 26907U 01040C   06004.70828653  .00000010  00000-0  18201-4 0    08
    2 26907  63.4290 242.5838 0005000  90.3926 269.6074 13.40483231    09
    
                                                           1030 X 1182 km
    1 26907U 01040C   09065.13822978  .00000020  00000-0  35283-4 0    09
    2 26907  63.4323 181.1938 0102000   1.2351 358.7650 13.40534122    02
    
    Ted Molczan
    
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